I think the next aircraft should depend on the development of the game. Is there a heavy gate already implemented? If so a widebody (possibly with two front doors to test two jetway gates) would be the best.
In my opinion the A330-200 would be the best, because we dont have Airbus yet.

I must say I am not a huge fans of the Twin Otters or the Cessna Caravans. Not as planes as such but for them being used in actual airline service. I know they are used in the Maldives and in the Seychelles but I have never really seen them in Europe (where I live). I would like it more if they would just be used for the GA and not really pull up to actual gates.